Manufacture of polymeric acids



P No Drawing. Filed Jan. 20, 1959, Ser. No. 787,809 Claims priority, application Great Britain Jan. 21, 1958 9 Claims. (Cl. 260-407) The present invention concerns improvements in or relating to the manufacture of polymeric acids. More particularly, it relates to the polymerisation of polyunsaturated fatty acids which at least partly consist of acids with conjugated double bonds to yield products consisting predominately of dimeric acids.

It is known to make dimeric acids by heat-polymerisation of polyunsaturated fatty acids but the products obtained consist mainly of a mixture of dimeric and trimeric acids, together with unpolymerised monomeric acids. If it is desired to obtain a product consisting mainly of dimeric acids, then clearly it is necessary to choose conditions which prevent the formation of trimeric acids as much as possible. This problem is particularly important in the polymerisation of polyunsaturated fatty acids which consist, at least partly, of acids with conjugated double bonds, such as dehydrated castor oil fatty acids or isomerised soya bean oil fatty acids, or other isomerised fatty acids with a high linoleic acid content, such as tall oil fatty acids or safilower oil fatty acids because in this case there is a pronounced tendency for formation of trimeric acids to prevail.

It has now been found it is not only possible to polymerise polyunsaturated fatty acids to give products containing only moderate amounts of tlimeric acids, but also at the same time to achieve better yields than those obtained by the known process.

According to the present invention there is provided a process for the heat-polymerisation under pressure of polyunsaturated fatty acids having a chain length corresponding to the natural fat acids and which at least partly consist of acids with conjugated double bonds in which the polymerisation is effected in a plurality of stages and in which, after each stage, the unpolymerised acids are recovered by vacuum distillation, the next stage of the polymerisation being carried out on the distillate.

Whilst the polymerisation process may be divided into any number of stages it is preferable to use a two-stage process. In the first stage the polymerisation is discontinued when only a portion of the raw material, e.g. one third or half, has been polymerised. Each polymerisation stage may be carried out under more severe conditions of time and/or temperature than the immediately preceding stage, especially if very mild conditions are used in the first stage. In the final stage the conditions must be severe enough to give a satisfactory overall yield, but not too severe so as to endanger the quality of the product.

It has been found that very little decarboxylation occurs if polyunsaturated fatty acids of the above type are heatpolymerised in a pressure vessel. The pressure required is relatively low, e.g. 65 psi at 300 C. will give a product having an acid value of at least 180. The pressure may be generated quite simply by means of the heat expansion of the acid used as raw material, and this is the preferred method of the invention. It is found that the acid value of the product depends, apart from the polymerisation temperature, on the ratio of the amount of the initial charge to the capacity of the pressure vessel. That is to say, the more material charged to the autoclave, i.e. the higher the pressure, the nearer the acid value of the polymeric acid approaches 190, which is known as the practical limit. By means of preliminary 3,059,03 Patented Oct. 16, 1962 tests the minimum initial charge necessary to give an acid value of at least 180 for a given material at a given temperature can be determined. Thus, for example, if the polymerisation is carried out at 300 C. and the pressure vessel is filled at room temperature to about 60% of its capacity, this gives rise to a pressure of about 30 to p.s.i., according to the raw material to be polymen'sed.

It has been found that in an autoclave filled with raw material as usually as much as possible to its maximum capacity, pressures are generated which, under the high polymerisation temperatures, suffice to secure acid values of at least 180.

In the experiment, the results of which are summarised in Table I below, dehydrated castor oil fatty acids of about 50% conjugation were heated in an autoclave to the polymerisation temperature for a given time. The autoclave was filled to 60% of its capacity. Afterwards the polymerisate was distilled in a vacuum of 2 millimeters of mercury until the still temperature reached 285 C. The yield, as shown in Table I, was calculated as a percentage of the raw material used and the viscosity of the residue was determined at 25 C. Since the viscosity increases parallel with the trimer content of the products, provided the removal of the monomeric acids has always been done under strictly identical conditions, the viscosity figures give a fair indication of the tr-imeric acid content of the polymerised fatty acid.

The dehydrated castor oil fatty acids were then treated by the process of the invention in which they were heated to 300 C. for 1 /2 hours whereafter the monomeric acids were removed by distillation. The distillate was polymerised once more at 300 C. for 1 /2 hours and freed from monomeric acids as described above. The distillate was subjected to a third polymerisation at 300 C. for 1 /2 hours and the reaction mixture worked up as described. The results obtained are summarised in the following Table II:

Table II Polymeric Acids Amount of Stage Material, Yield (perparts cent de- Acid Viscosity hydrated Value in Stokes castor oil at 25 0. fatty acids) In another process according to the invention only two stages Were used. In stage I the polymerisation was carried out at 300 C. for one hour, in stage 11 (using the distillate of the polymerisate of stage 1 as raw material) at 325 C. for 2 hours, with the results summarised in the following Table III.

If the acid obtained by caustic alkali treatment of soya bean oil fatty acids (at 180 C.) was heated to 325 C. for

three hours in an autoclave filled to 55 w./v. percent of its capacity, subsequently removing the monomeric acids by vacuum distillation, the distillation residue amounted to 41.2% of the isomerised acid which has a very high viscosity (164.9 stokes at 25 C.) and an acid value of 183.5.

The isomerised acid was then treated by the process of the invention in which it was heated to 310 C. for one hour in an autoclave filled to 65 w./v. percent of its capacity. V Afterwards, the non-polymerised acids, which were removed by distillation from the dimeric acids, were once .more polymerised at 330 C. for two hours in an autoclave filled to 55 w./v. percent of its capacity. The monomeric acids were distilled OE and thus dimeric acids were obtained. The total yield of dimeric acids amounted to 49.3%. The viscosity of this product is only 104 stokes at 25 C. and the acid value 181.2.

Thus by the use of the process of the present invention product can be obtained which, by comparison with 7 having a chain length corresponding to the natural fat acids and which at least partly consist of acids with conjugated double bonds comprising subjecting said polyunsaturated fatty acids to a series of at least two stages including a last stage, each stage comprising heating at a temperature of about 280 C. to about 360 C. s'aidpolyunsaturated fatty acids under pressure resulting from said heating at a polymerization temperature for said fatty acids for a period of time ranging from about 1 to 3 hours sufiicient to polymerize a portion of said fatty acids to dimeric acids, removing the remainder of the nonpolymerized fatty acids, and subjecting said remainder to the aforesaid stage. 7

2. The process as defined in claim 1 wherein the pressure is from about 30 to 75 p.s.i.

3. The process as defined in claim 1 wherein the pressure is 65 p.s.i.

4. The process as defined in claim 1 wherein the portion of the polyunsaturated fatty acids which is polymerized at each stage to dimeric acids is from about onethird to one-half of said fatty acids.

5. The process as defined in claim 1 wherein said removing of the remainder of the non-polymerized fatty acids is a vacuum distillation.

6. The process as defined in claim 1 wherein the acid value of the resulting products is at least "180.

7. The process as defined in claim 1 wherein said 7 polyunsaturated fatty acids are selected from the group consisting of dehydrated castor oil fatty acids, isomerised soya bean oil fatty acids, tall oil fatty acids and safiiower oil fatty acids.

8. A process for forming products consisting predominantly of dimeric acids from polyunsaturated fatty acids having a chain length corresponding to the natural fat acids and which at least partly consist of acids with conjugated double bonds comprising subjecting said polyunsaturated fatty acids to a series of at least two stages, each stage comprising heating said polyunsaturated fatty acids under pressure resulting from the heating of said fatty acids at a temperature of about 300 C. for a period of about one hour, removing the remaining non-polymerized fatty acid by vacuum distillation, and repeating said stage with the distillate at a temperature of about 325 C. for a period of about two hours.

9. The process as defined in claim 1 wherein said polyunsaturated fatty acids are selected from the group consisting of dehydrated castor oil fatty acids, isomerised soya bean oil'fatty acids, tall oil fatty acids and saffiower oil fatty acids, and repeating said stage with the distillate under more severe reaction conditions sufficient to give a satisfactory over-all yield but insufficient to endanger the quality of the dimeric acid products.

Oosterhof et a1 Dec. 29, 1936 Briscoe July 18, 1939 

1. A PROCESS FOR FORMING PRODUCTS CONSISTING PREDOMINANTLY OF DIMERIC ACIDS FROM POLYUNSATURATED FATTY ACIDS HAVING A CHAIN LENGTH CORRESPONDING TO THE NATURAL FAT ACIDS AND WHICH AT LEAST PARTLY CONSIST OF ACIDS WITH CONJUGATED DOUBLE BONDS COMPRISING SUBJECTING SAID POLYUNSATURATED FATTY ACIDS TO A SERIES OF AT LEAST TWO STAGES INCLUDING A LAST STAGE, EACH STAGE COMPRISING HEATING AT A TEMPERATURE OF ABOUT 280*C. TO ABOUT 360*C. SAID POLYUNSATURATED FATTY ACIDS UNDER PRESSURE RESULTING FROM SAID HEATING AT A POLYMERIZATION TEMPERATURE FOR SAID FATTY ACIDS FOR A PERIOD OF TIME RANGING FROM ABOUT 1 TO 3 HOURS SUFFICIENT TO POLYMERIZE A PORTION OF SAID FATTY ACIDS TO DIMERIC ACIDS, REMOVING THE REMAINDER OF THE NONPOLYMERIZED FATTY ACIDS, AND SUBJECTING SAID REMAINDER TO THE AFORESAID STAGE. 